Firstly, as an example of the related art, a description will be given of a multi-user MIMO (Multiple-input multiple-output) in single-carrier transmissions which use guard intervals (GI). The related art includes a single user MIMO in a single-carrier transmission (for example, see Non-patent documents 1 and 2). Note that this related art can easily be expanded to a multi-user MIMO system.
FIG. 18 is a block diagram showing a structural example according to the related art of a uth single-carrier transmitter in a multi-user MIMO transmission which uses GI. FIG. 19 is a block diagram showing a structural example according to the related art of a single-carrier receiver in a multi-user MIMO transmission which uses GI.
Here, the number of transmitting stations (i.e., terminal stations: MT) is U, and the number of signal sequence (i.e., transmitter antenna) of the uth transmitting station is nt (u). Moreover, the number NT of the total transmitted signal sequence at a receiving station is expressed by the following formula.
                    [                  Formula          ⁢                                          ⁢          1                ]                                                            NT        =                              ∑                          u              =              1                        U                    ⁢                      nt            ⁡                          (              u              )                                                          (        1        )            
Moreover, the number of receiver antennas at an access point (AP) is NR (wherein NR≧NT), and the number of discrete Fourier transform points is taken as N. The GI length is taken as Ng.
In the uth transmitter of a conventional single-carrier transmission such as that shown in FIG. 18, 100-u is an error correction encoding section, 101-u is an interleaver, 102-u is a data modulation section, 103-u is a serial-to-parallel conversion section, 104-u-1 through 104-u-nt (u) are GI insertion sections, 105-u-1 through 105-u-nt (u) are waveform shaping sections, 106-u-1 through 106-u-nt (u) are D/A converters, 107-u-1 through 107-u-nt (u) are radio sections, and 108-u-1 through 108-u-nt (u) are transmitter antennas.
In the uth transmitting station shown in FIG. 18, after the series has been encoded by the channel encoder 100-u, it undergoes interleaving in the interleaver 101-u, and then undergoes modulation by means of PSK (Phase Shift Keying) or QAM (Quadrature Amplitude Modulation) in the data modulation section 102-u, so that a transmitted symbol sequence is thereby created. Thereafter, the symbol sequence is divided into nt (u) streams which is the same as the number of antennas by the serial-to-parallel conversion section 103-u, and one block is formed for each N symbol by the GI insertion sections 104-u-1 through 104-u-nt (u). The Ng symbol at the end of the block is then copied, and is inserted as a GI, as is shown in FIG. 22.
Next, the symbol sequence undergoes waveform shaping (i.e., undergoes digital filtering to limit bandwidth) in the waveform shaping sections 105-u-1 through 105-u-nt (u), and then undergoes digital/analog conversion in the D/A converters 106-u-1 through 106-u-nt (u). The symbol sequence is then transmitted by the nt (u) number of transmitter antennas 108-u-1 through 108-u-nt (u) via the radio sections 107-u-1 through 107-u-nt (u).
Moreover, in a receiver at an AP in a conventional single-carrier transmission such as that shown in FIG. 19, 110-1 through 110-NR are receiver antennas, 111-1 through 111-NR are radio sections, 112-1 through 112-NR are A/D converters, 113-1 through 113-NR are GI removal sections, 114-1 through 114-NR are discrete Fourier transformers, 115-1 through 115-N are multi-user detectors, 116-1 through 116-NT are inverse discrete Fourier transformers, 117-1 through 117-U are parallel-to-serial converters, 118-1 through 118-U are data demodulators, 119-1 through 119-U are deinterleaver circuits, and 120-1 through 120-U are error correction decoding sections.
In FIG. 19, single-carrier transmitted signals are received by the NR number of receiver antennas 110-1 through 110-NR, and are converted into a baseband signal for each antenna by the radio sections 111-1 through 111-NR. They then undergo analog/digital conversion in the A/D converters 112-1 through 112-NR, and the GI is then removed by 113-1 through 113-NR. Thereafter, the received signals are split into N number of frequency components by the discrete Fourier transformers 114-1 through 114-NR, and signal separation is then performed in the multi-user detectors 115-1 through 115-N using the NR number of received signals as input values for each frequency component. As a result, a total number of NT transmitted signal streams is obtained as an output value.
Next, after multi-user detection has been performed by the multi-user detectors 115-1 through 115-N, the signals are inserted into time signals using the inverse discrete Fourier transformers 116-1 through 116-NT, and are then converted into time series signals for each transmitting station by the parallel-to-serial converters 117-1 through 117-U. Finally, data demodulation, deinterleaving, and error correction decoding are performed by the data demodulators 118-1 through 118-U, the deinterleavers 119-1 through 119-U, and the error correction decoders 120-1 through 120-U.
Next, multi-user MIMO (Multiple-input multiple-output) in multicarrier transmissions which use guard intervals (GI) will be described as an example of the related art (see, for example, Non-patent document 3).
FIG. 20 is a block diagram showing a structural example of a uth multicarrier transmitter in a multi-user MIMO transmission which uses GI of the related art. FIG. 21 is a block diagram showing a structural example of a multicarrier receiver in a multi-user MIMO transmission which uses GI of the related art.
Here, the number of transmitting stations (i.e., terminal stations: MT) is U, and the number of signal sequence (i.e., transmitter antenna) of the uth transmitting station is nt (u). Moreover, the total number of NT transmitted signal sequence in the receiving station is expressed in the same way as in Formula (1) given above.
Moreover, the number of receiver antennas at an access point (AP) is NR (wherein NR≧NT), and the number of discrete Fourier transform points (i.e., the number of subcarriers) is taken as Nc. The GI length is taken as Ng.
In the uth transmitter of a conventional multicarrier transmission such as that shown in FIG. 20, 201-u is an error correction encoding section, 202-u is an interleaver, 203-u is a first serial-to-parallel conversion section, 204-u-1 through 204-u-nt (u) are first serial-to-parallel conversion sections, 205-u-1-1 through 205-u-nt (u)-Nc are data modulation sections, 206-u-1 through 206-u-nt (u) are inverse discrete Fourier transformers, 207-u-1 through 207-u-nt (u) are GI insertion sections, 208-u-1 through 208-u-nt (u) are waveform shaping sections, 209-u-1 through 209-u-nt (u) are D/A converters, 210-u-1 through 210-u-nt (u) are radio sections, and 111-u-1 through 111-u-nt (u) are transmitter antennas.
In the uth transmitting station shown in FIG. 20, after the transmission data sequence has been encoded by the error correction encoding section 201-u, the transmission data undergoes interleaving in the interleaver 202-u. The data sequence is then made to undergo serial-to-parallel conversion into the same number of streams as the number of antennas (which is nt (u)) by the first serial-to-parallel converter 203-u. Each of these streams is then made to undergo further serial-to-parallel conversion in the second serial-to-parallel converters 204-u-1 through 204-u-nt (u), and the data string is split into Nc series which is the number of subcarriers. Modulation is then performed in the respective subcarriers based on PSK (Phase Shift Keying) or QAM (Quadrature Amplitude Modulation) by the data modulation sections 205-u-1-1 through 205-u-n (u)−Nc.
Thereafter, multicarrier signals are created by the inverse discrete Fourier transformers 206-u-1 through 206-u-nt (u), and a sample of the last multicarrier signal Ng is copied by the GI insertion sections 207-u-1 through 207-u-nt (u), and is inserted as a GI as is shown in FIG. 22. After waveform shaping has been performed by the waveform shaping sections 208-u-1 through 208-u-nt (u), and D/A conversion has been performed by the D/A converters 209-u-1 through 209-u-nt (u), the signals are transmitted by the nt (u) number of transmitter antennas 211-u-1 through 211-u-nt (u) via the radio sections 210-u-1 through 210-u-nt (u).
Moreover, in a receiver of a conventional multicarrier transmission such as that shown in FIG. 21, 220-1 through 220-NR are receiver antennas, 221-1 through 221-NR are radio sections, 222-1 through 222-NR are A/D converters, 223-1 through 223-NR are GI removal sections, 224-1 through 224-NR are discrete Fourier transformers, 225-1 through 225-Nc are multi-user detectors, 226-1 through 226-Nc-NT are data demodulators, 227-1 through 227-NT are first parallel-to-serial converters, 228-1 through 228-U are second parallel-to-serial converters, 229-1 through 229-U are deinterleaver circuits, and 230-1 through 230-U are error correction demodulation sections.
In FIG. 21, multicarrier transmitted signals are received by the NR number of receiver antennas 220-1 through 220-NR, and they are then converted into baseband signals in each antenna by the radio sections 221-1 through 221-NR. They are then made to undergo analog/digital conversion in the A/D converters 222-1 through 222-NR, and the GI is removed by 223-1 through 223-NR. Thereafter, the received signals are broken down into Nc number of multicarriers by the discrete Fourier transformers 224-1 through 224-NR, and using the NR number of received signals as input values, the received signals are made to undergo signal separation in the multi-user detectors 225-1 through 225-N in each subcarrier. As a result, a total number of NT transmitted signal streams are obtained as output values.
Next, after multi-user detection has been performed by the multi-user detectors 225-1 through 225-Nc, data demodulation is performed in each subcarrier by the data demodulators 226-1-1 through 226-Nc-NT. The signal sequence is then made to undergo parallel-to-serial conversion using the first parallel-to-serial converters 227-1 through 227-NT, and is then further converted into signal sequence for each transmitting station by the second parallel-to-serial converters 228-1 through 228-U. Finally, deinterleaving and error correction decoding are performed by the deinterleavers 229-1 through 229-U and by the error correction decoders 230-1 through 230-U.    [Non-patent document 1]: “Transmission Performance Evaluation of Single-Carrier MIMO Multiplexing”, Akinori Nakajima, Garg Deepshikha, and Fumiyuki Adachi, IEICE Tech. Rep., RCS2004-107, pp. 13-18, August 2004.    [Non-patent document 2]: “Adaptive Frequency-Domain Equalization for Single-Carrier Multiple-Input Multiple-Output Wireless Transmissions”, J. Coon, S. Armour, M. Beach, and J. McGeehan, IEEE Trans. Signal Processing, vol. 53, pp. 3247-3256, August 2005.    [Non-patent document 3]: “Fundamental Studies on MIMO-OFDM Space Division Multiplexing”, Nishio, Ogawa, Nishimura, and Ohgane, IEICE Tech. Rep., IEICE, DSP2002-204, SAT-2002-154, RCS2002-273, January 2003.